Many owners will swap the 1.1 Bar rated radiator cap that comes stock on the XR650R for an aftermarket unit. The goal is the prevent the radiators from boiling over as easily. It’s a somewhat debated topic in that using a higher pressure cap will increase the strain throughout the entire system. Most have positive experiences with switching radiator caps. Personally, I prefer to keep mine stock.
The 1992-1996 Kawasaki KX500 Radiator cap is 1.8 Bar and can be swapped directly onto the XR650R. The Kawasaki part number is: 49085-1059